1. Field of the Invention
The present invention relates to an electrophotographic apparatus such as a copying apparatus, and a method of cleaning a photosensitive member in the electrophotographic apparatus.
2. Description of the Related Art
An electrophotographic apparatus includes a photosensitive member, such as a photosensitive drum or a photosensitive belt member, on which a latent image is formed by an exposing operation and then a toner image is formed by a developing operation. The tonner image is transferred to a recording sheet directly or via a transferring member from the photosensitive member.
Accordingly, it is desirable to transfer all the toner of the toner image from the photosensitive member to the recording sheet. However, a certain amount of the toner of the toner image is remained to be attached on the photosensitive member after this transferring operation.
Thus, the electrophotographic apparatus is equipped with a cleaning device which removes such undesirable residual toner from the photosensitive member. The cleaning device also removes corona products, paper or sheet powders, and an ozone degraded layer formed at the extreme surface of the photosensitive member. The corona products are formed during the charging process of the photosensitive member, while the ozone degraded layer is formed during the transferring process.
In case that the photosensitive member is made from the organic photosensitive compound (OPC), such a cleaning operation becomes very important, since the above mentioned residual toner etc. affects and degrades the image quality to a great extent in this case.
As one type of such cleaning devices, there is a blade cleaning type, which cleans the photosensitive member by pressing a blade onto the photosensitive member after the electrophotographic operation, so as to scrape off the residual toner etc. from the photosensitive member.
However, the cleaning ability of above mentioned cleaning method is not always sufficient. Especially, in case of a high speed copying apparatus and a full color copying apparatus, the above mentioned cleaning method is not enough. Namely, in case of the high speed copying apparatus, the corona products and the sheet or paper powders are generated in a great amount. In case of the full color copying apparatus, the toner is relatively difficult to remove from the photosensitive member in which filming of the toner easily occures due to its low melting point. Thus, in these apparatuses, since the above mentioned cleaning method is not enough, the quality of the outputted image is degraded by the residual toner etc. while the photosensitive member is easily damaged by these undesirable existences.
The above mentioned problem is enhanced in case that a large number of copying operations are continuously performed, which is quite normal case in the practical use. Thus, this mentioned problem is practically a quite serious one.
As a countermeasure for this problem, the pressure of the cleaning blade against the photosensitive member may be increased so as to increase the cleaning ability. But, this turns out to cause another problem that the photosensitive member is damaged especially in case of the aforementioned OPC type photosensitive member, though this damage is not so serious in case of the amorphous selenium or amorphous silicon type photosensitive member which surfaces are relatively hard.
Consequently, inspite of a general demand to improve the image quality of the electrophotographic apparatus, image defects such as fogging and voiding in the outputted image, are caused by these residual toner etc. because a sufficient cleaning method is not realized.